Herpes Zoster (HZ) is estimated to affect between 600,000 to 1 million people annually in the United States. The incidence and severity of HZ, as well as the frequency and severity of its complications, increase markedly with age. Antiviral therapy has modest impact on the acute phase of HZ. However, it does not appear to prevent post herpetic neuralgia, the most common complication of HZ. During the past decade studies have revealed a close temporal relation between the age-related increase in the incidence and severity of HZ and an age-related decline in cell mediated immunity to varicella-zoster virus (VZV). The administration of a live attenuated varicella-zoster vaccine to older adults results in a marked and long lasting increase in VZV-specific cell-mediated immunity. We hypothesize that by boosting VZV-specific cellular immune responses, the incidence and severity of HZ and its complications can be reduced. This a double-blind, placebo-controlled multicenter trial to determine whether immunization with a live attenuated varicella-zoster virus vaccine decreases the incidence and severity of HZ and its complications in adults 60 years of age and older. The enrollment phase was completed on July 31, 2001 at all sites, but San Diego and Denver. As of July 31, 2001, 38,341 individuals had been vaccinated nationwide. Of these, 1,741 volunteers were enrolled at the NIH Bethesda site. The follow up period will continue for approximately 3 and half years. To date, 27 suspected cases of herpes zoster have been evaluated at the NIH Clinical Center. The Data Safety and Monitoring Board (DSMB) is meeting on regular basis and at its last meeting in July 2002 the board concluded that the distributions of serious adverse experiences by treatment group (vaccine vs placebo) did not suggest any vaccine related safety problems